The present invention relates to sensing elements and trim resistors and methods of using the same.
Sensors are positioned to monitor variables such as exhaust gases of an exhaust system. In most applications the sensors, which are exposed to the exhaust gases are typically associated with a controller comprising microelectronics in order to receive signals from the sensors and provide signals and/or commands to components of another system. Some sensors require a compensation resistor or trim resistor to be associated with the sensor and the electronics of the system in order to provide signals to the controller of the system in order to compensate for part-to-part variability in the sensor itself.
For example, and since some sensors cannot be made accurate enough to be used as made, a trimming resistor is employed to inform the controller how a particular sensor varies from the ideal sensor. Accordingly, the sensor with the trim resistor allows the system to accurately measure a particular constituent (e.g., sensor+trim resistor+controller).
In the past, there have been two ways to do this. The first being the incorporation of a trim resistor into the interface circuit of the microprocessor of the sensor system such that the circuit topology of the sensor system and the interface together includes the trim resistor as part of the active circuit that is amplifying the sensor signal. The trimmed resistor can then change a gain, offset or time constant in the interface to match the electronic interface performance to a specific sensor. This method is traditionally used in a purely analog interface.
The second method is more typically associated with an interface that utilizes a digital signal processing approach. In this method the actual sensor outputs are read by the digital interface in their raw, uncorrected form and then these raw values are normalized by a correction algorithm. In this application the trim resistor is read in as a separate input and its value is used as an input in a correction algorithm, which is performed by software. In this application, the trim resistor controls the correction however, it is not part of the main signal path from the actual sensor inputs.
In both of the aforementioned methods and/or processes one trim resistor is used for each parameter to be normalized. Thus, multiple trim resistors are required for multiple sensor inputs.
Accordingly, it is desirable to provide a sensor wherein two or more compensation values may be determined with a single trim resistor.